The revised plan is laid out for regulators at the Federal Communications Commission in filings that seek a lower orbit for 1,584 of the more than 4,400 satellites it envisions launching. The new target orbit would be 550 kilometers (342 miles) in altitude, as opposed to the 1,150-kilometer (715-mile) orbit described in SpaceX’s initial round of filings.

Those spacecraft, which were built at SpaceX’s satellite development facility in Redmond, Wash., have been undergoing testing for months. Some observers wondered why the Tintin satellites weren’t sent into a higher orbit as planned — and the revised constellation plan could provide an explanation.

“This move will help simplify the spacecraft design and enhance the considerable space safety attributes of SpaceX’s constellation by ensuring that any orbital debris will undergo rapid atmospheric re-entry and demise, even in the unlikely event that a spacecraft fails in orbit,” SpaceX said in the documents filed today.

SpaceX said the plan for a lower orbit means 16 fewer satellites will be required — and will also reduce the potential for a traffic jam at the higher orbit, which is close to the altitude targeted by rival broadband constellations being considered by OneWeb, Boeing and Telesat.

Starlink will require thousands of satellites because each satellite spends only a few minutes in contact with a given ground station as it passes over. But once enough satellites are in orbit, the constellation should provide global coverage, theoretically making low-cost broadband internet access available to billions of people who don’t have it today.

Having the satellite in low Earth orbit as opposed to a much higher geostationary orbit reduces the lag time, or latency, for data transmissions. In May, SpaceX CEO Elon Musk said the response time for the Tintin satellites was “pretty good,” with latency amounting to 25 milliseconds. “Good enough to play fast-response video games,” he tweeted.

When the low-orbit constellation is fully deployed, latency could be reduced to as little as 15 milliseconds, “at which point it would be virtually unnoticeable to almost all users,” SpaceX said in today’s filing.

SpaceX acknowledged that going lower will present some challenges. At least at first, the satellites will have to widen their transmission angles so that ground stations can be in communication when the satellites are just 25 degrees above the horizon, as opposed to 40 degrees under the original plan.

Also, SpaceX has to convince the FCC that the revised plan would create no more interference for ground-based networks and geosynchronous satellite networks than the original plan would have. The company presented pages of graphs showing that would be the case.

SpaceX clearly wants the FCC to expedite approval of the revisions: When the agency gave its original approval, it said the thumbs-up was contingent on favorable findings from the International Telecommunications Union, the global authority on telecom satellite orbits. But in today’s filings, SpaceX said it wasn’t optimistic about getting the ITU’s go-ahead on a timely schedule. It offered orbital data based on ITU simulations as a substitute, in hopes of getting a waiver of the FCC’s original requirement.

SpaceX said it was planning to beat the deadlines laid out by the FCC in its original approval. “SpaceX intends to launch its first batch of satellites to begin populating a new orbital shell before the end of 2019,” it said. At least half of the 4,400-plus satellites are required to be in operation by March 29, 2024.

In today’s filings, SpaceX gave a shout-out to its Redmond operation, which recently underwent a reorganization to accelerate the pace of satellite development. “SpaceX was able to move from opening its satellite technology development office in Redmond, Washington, to building, launching and operating its own spacecraft in orbit in an unprecedented three and a half years,” the company said.

In other SpaceX news:

NASA’s Launch Services Program has certified SpaceX’s Falcon 9 rocket as a Category 3 launch vehicle. Such vehicles are certified to support NASA’s highest cost and most complex scientific missions. “LSP Category 3 certification is a major achievement for the Falcon 9 team and represents another key milestone in our close partnership with NASA,” SpaceX President Gwynne Shotwell said in a statement. “We are honored to have the opportunity to provide cost-effective and reliable launch services to the country’s most critical scientific payloads.”

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